Mast cells are known for their role in allergy, asthma, autoimmunity, hypersensitivity responses and increase inflammation. However, mast cells can limit inflammation and tissue injury. These and other findings suggest that mast cells occupy a critical niche at the interface of innate an acquired immunity, where, depending on circumstances, mast cells may function to perturb or help to restore homeostasis, with consequences that can either promote health or contribute to disease. In this work we aim to explain the importance of mast cells in the immune response using four examples of pathologies in which these cells are involved: Allergy, Asthma, Irritable bowel Syndrome (IBS) and the response to nematodes such as Trichinella Spiralis.